Global navigation satellite systems (GNSS) are widely used for high-precision positioning, such as the US Global Positioning System (GPS) and Russian global navigation system GLONASS, as well as some others. A GNSS antenna has to provide signal reception in the whole GNSS range, namely, a low-frequency band 1164-1300 MHz and high-frequency band 1525-1610 MHz.
One of the most important positioning errors in GNSS systems is a so-called multipath error, when a signal reflected from the underlying ground surface appears at the input of the receiving antenna along with the line-of-sight signal.
The value of the multipath error is proportional to the ratio
      DU    ⁡          (      θ      )        =            F      -              (        θ        )                    F      ⁡              (        θ        )            
This ratio is normally called the Down/Up ratio. In this ratio, θ is the elevation angle over the horizon, and F(+/−θ) is the antenna pattern (AP) at angle θ above and under the local horizon (θ=0°) correspondingly. A spatial region where θ>0 is the upper or front hemisphere, otherwise, a spatial region at θ<0 is called the lower or backward hemisphere.
To provide a stable and reliable operation of positioning systems, quality signal reception from all satellites over the local horizon is required. The value F(θ) in the upper hemisphere is not to highly vary. At the same time, the value F(θ) in the lower hemisphere should be as small as possible. So the value F(θ) should have a sharp drop in the vicinity of the local horizon (i.e., near θ=0°).
Receiving antennas thus need to provide such an AP whose level is negligibly varied in the upper hemisphere, sharply drops in crossing the direction to the local horizon, and is small in the lower hemisphere. Also, such an antenna pattern needs to be provided over whole operational frequency range.